Tunable filters for spectral sensing

ABSTRACT

A spectroscopic analysis device for analysis of a sample comprises an input for receiving light from the sample and a photonic integrated circuit. This photonic optical filter comprises one or more tunable bandpass filters arranged to filter the received light. Furthermore, the device comprises a controller that is arranged—to control the one or more tunable bandpass filters, to receive filter results obtained from the one or more tunable bandpass filters, and to provide spectroscopic analysis results based on the received filter results.

CROSS REFERENCE TO PRIOR APPLICATIONS

This application is a Continuation of U.S. Ser. No. 15/125,686, filedSep. 13, 2016, which is the U.S. National Phase application under 35U.S.C. § 371 of International Application No. PCT/EP2015/055251, filedon Mar. 13, 2015, which claims the benefit of European PatentApplication No. 14160522.0, filed on Mar. 18, 2014 and European PatentApplication No. 14178156.7, filed on Jul. 23, 2014. These applicationsare hereby incorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to a spectroscopic analysis device for analysis ofa sample based on light received from the sample. Furthermore, theinvention relates to the spectroscopic analysis and characterization oftissue.

BACKGROUND OF THE INVENTION

Devices for spectral tissue sensing and for other spectral sensingmethods include a broadband light source and one or more broadbandspectrometers. In practice, two of these are included because of theneed to cover both the visible and the near infrared wavelength ranges.Example prior art for Spectral Tissue Sensing are disclosed inInternational Patent Applications WO2012/127378, WO2012/093309 andWO2013/001423. International Patent Application WO2011/132128 disclosesan example where a limited number of wavelengths are used to detectwater and lipid.

This Spectral Tissue Sensing has a great potential in many applicationareas, especially in the medical applications area. However, to become asuccess, both cost and form factor are of high importance. Current stateof the art technology still requires systems that need to be transportedon a separate cart and that involve high cost. The result is that thesesystems are only used in a hospital environment, where only a limitednumber of such devices will fit in the budget and workflow.

Document US20120226118A1 discloses an implantable sensor for sensing asubstance such as glucose. The sensor comprises a photonic integratedcircuit based radiation processor for spectrally processing radiationinteracting with the sample.

Document US20070109550A1 discloses a system and method for detecting theoptical spectrum of an optical input signal. The system includes atunable optical filter having a microresonator that is tunable across aplurality of states and a processor. The input signal is coupled intothe microresonator, which is continuously tuned across a spectral rangethat is narrow relative to the targeted detection range.

Document US2009/0245796 relates to the optical communications field anddiscloses a planar lightwave circuit that includes a substrate, atunable filter, a demultiplexer, and an optical processor each disposedon the substrate. The tunable filter is configured to filter at leastone of a bandwidth or a wavelength of a Wavelength Division Multiplexedoptical input signal. The demultiplexer is connected to the tunablefilter and configured to receive a filtered Wavelength DivisionMultiplexed optical input signal at an input and to supply one of aplurality of channels of the filtered Wavelength Division Multiplexedinput signal at a respective one of a plurality of outputs. Each of theplurality of channels corresponds to one of a plurality of wavelengthsof the filtered Wavelength Division Multiplexed input signal. Theoptical processor includes a bit-delay interferometer communicating witha respective one of the plurality of outputs of the demultiplexer. Theoptical processor is configured to receive one of the plurality ofchannels from the demultiplexer and output a plurality of demodulatedoptical signal components.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a spectroscopicanalysis system that mitigates one or more of the problems related tothe current systems. To this end, the invention provides a spectroscopicanalysis device for analysis of a sample comprising: an input forreceiving light from the sample, a photonic integrated circuitcomprising one or more tunable bandpass filters arranged to filter thereceived light, and a controller arranged to control the one or moretunable bandpass filters, to receive filter results obtained from theone or more tunable bandpass filters, and to provide spectroscopicanalysis results based on the received filter results.

An important element of the invention is the combination of fastdetection and high resolution through tunable filters (for exampleresonators) on a photonic integrated circuit (PIC) with small broadbandlight source and a simple microcontroller. Fast detection is achievedbecause a limited number of wavelengths is measured simultaneously in avery narrow band per measurement. As a result of this, simple, low noisephoto detectors can be used meaning that the dominant noise contributionis only the shot noise of the incoming light. To achieve a sufficientSNR of 40, only 1600 photons are needed meaning extremely fastmeasurement times. By combining fast tunable optical filters withappropriate classification algorithms, currently known diagnosticdevices based on conventional spectroscopy are great improved, forexample for tissue recognition.

According to the invention, both the form factor and cost can be reducedsignificantly, enabling application for mobile devices. This will notonly broaden the application in the hospital, but also enables point ofcare application, and mobile or emergency services use. The capabilityof fast tuning (milliseconds) and high resolution (<0.1 nm) combinedwith sensitive photo detector and small size of the filter, allow forthe integration of a bank of filters on a single chip that is fed from asingle input signal.

Various types of tunable filters exist such as Fabry-Perot filters,acousto-optical tunable filters, Distributed Bragg Reflector opticalfilters (disclosed for example in U.S. Pat. No. 5,022,730), MEMS tunablefilters (e.g. of DiCon Fiberoptics Inchttp://www.diconfiberoptics.com/products/tunable_optical_filter.php) ortunable filters based on multivariate optical elements, as for exampledisclosed in International Patent Applications WO2004/057284,WO2006/114773. These known filters are either not sufficiently small toallow for the creation of a small spectroscopic analysis device, orsuffer from a too small tuning range or have other disadvantages.

Fast tunable optical filters are known in the domain oftelecommunications, see for example U.S. Pat. No. 6,901,178. With theadvent of photonic integrated circuits, the creation of such filters ata low cost is now feasible on a substrate. In addition, the small sizeof the filter results in low time constants allowing for faster tuning.Such filters can be combined into more complex circuits, such as forexample shown in the article of A. Meijerink et al., “Novel ringresonator-based integrated photonic beamformer for broadband phasedarray receive antennas—part I: design and performance analysis”, Journalof Lightwave Technology, 2010, 28 (1). pp. 3-18. ISSN 0733-8724 and aretherefore regarded of interest for application in the telecommunicationsarea.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows an embodiment of the device according to the invention, and

FIG. 2 shows a further embodiment comprising attenuators.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows an embodiment combining a light source (e.g. tungstenhalogen exemplified by a 4 W Tungsten Halogen light source 4WTHS, LED orlaser) with a photonic integrated circuit PIC containing a beam splitter(for example an arrayed waveguide grating (AWG)) and a number of tunablefilters (consisting of for example ring cavity resonators), a photodetector per tunable filter output, an electronic integration circuitINT1 . . . INT3 for integrating the photo detector output over time, amultiplexing AD converter MUXADC and a microcontroller MC having amemory MWCWT (Memory with Coefficients and Wavelengths Table) configuredto store the relevant wavelength ranges and corresponding spectralcoefficients. A battery BAT for powering the device so that it can beused as a handheld device HHD is also illustrated in FIG. 1. To outputthe data, the device can be equipped with its own display, or controlledvia for example a smartphone, smart watch or tablet computer using forexample Bluetooth. This functionality is exemplified by Display orCommunications Interface D/CI in FIG. 1. The tuning is dependent on thetype of ring resonator used, and can for example be thermal, by tuningan optical delay line or by for example the electro-optical, thermooptical or acousto-optical changing of a refractive index. See forexample the article by Roeloffzen et al, “Silicon Nitride microwavephotonic circuits”, OPTICS EXPRESS 22937, Vol. 21(19), 2013].

In operation, the micro controller MC activates the broadband lightsource 4WTHS. As a result, broadband light is output through theillumination fiber ILF to the optical probe towards the sample/object ofinterest. The object of interest scatters and absorbs parts of thelight. A part of the scatter light is captured by the detection fiberDEF.

The incoming light from the detection fiber is offered over the wholewavelength range of interest (e.g., 400-2000 nm in the visible and nearinfra-red range that is currently used) to the PIC. The beam splitter(e.g., an AWG) distributes the incoming light over multiple tunablefilters, each with its own wavelength tuning range. The tunable filteris a sharp bandpass filter, passing the light over a range of forexample 0.1-5 nm. The light passed through the tunable filter is coupledto a photo detector (for example a PIN diode for the visible light, oran InGaAs diode for the near infrared light). Photons converted by thephoto detector are accumulated as a charge in the integrators. Theoutputs of the integrators fed into a multiplexed AD converter MUXADCand translated to an electrical signal corresponding to the amount oflight detected.

Per substance of interest, a classifier is created beforehand throughdimension reduction of the measured spectral range that needs a limitednumber of data points across the spectrum (typically in the order of5-20 wavelength bands) to reliably detect the presence and amount ofthat substance. This is regardless of the type of classifier used. Foreach substance of interest, the wavelengths to which the filters shouldbe tuned and the spectral coefficients for that wavelength sub range arestored in the memory of the micro controller. The procedure followed bythe microcontroller then is:

Tune a filter to the start of the wavelength sub range to be integrated.

Reset the integrator.

Measure and store the accumulated charge in the integrator.

Optionally scan through the whole wavelength sub range if the subrangeis larger than the bandwidth of the tunable filter.

Stop measuring and read-out the accumulated charge using the ADconverter.

In the microprocessor or microctrontroller MC, calculate the resultingoutput as a tissue classification by multiplying each measured filtersignal with its spectral coefficient from the memory and calculating thefinal output as the sum of these intermediate filter results. Note thatthe complexity of the algorithm calculations is reduced tomultiplications and additions only, thus meaning that a simplemicrocontroller (e.g., an ARM-Cortex type) already can provide real-timebehavior at a small size and low power consumption. Note that thisapproach can handle complex classification algorithms based on positiveand negative contributions (for example regression vectors). Thisalgorithm uses tunable filters for the specific wavelength ranges wherethe contribution is non-zero. For a positive contribution, a positivecoefficient is used in the calculation, for the negative contribution, anegative coefficient is used. The final summation then combines thepositive and negative contributions in a single result.

After that, the next substance can be measured. Dependent on the numberof filters in the bank, optionally multiple substances can be measuredat the same time, or multiple components of a single substance measuredsequentially allowing for a large flexibility with respect to thesubstances to be classified.

The approach described here can be used in alternative ways:

Full Wavelength Range Spectroscopy implementation with selectableresolution: move a tunable filter across the wavelength range ofinterest in fixed steps corresponding to the desired resolution andmeasure the intensity with a photo sensor (e.g., silicon photo diode,InGaAs photo diode, photo multiplier (note that dependent on thedetector technology used one or more may be needed to cover the wholewavelength range)). In practice, useful when gathering initialinformation, or when for example connected to a tablet which executesthe more complex algorithms on this information.

Classification algorithms based on ratios. This algorithm uses two ormore wavelength bands. A tunable filter is configured for eachwavelength band of interest consisting of a band pass filter, photosensor. The resulting signals can be subtracted and/or divided toprovide an indication for the specific characteristic. Measurement speedand accuracy is only limited by the amount of light and the number ofbands used. The algorithm is not processor intensive because most of thecalculations are done with light in the PIC and only the final divisionand coefficient multiplication are done in the microcontroller.

In an alternative embodiment, the amount of calculation required on themicrocontroller can be reduced even more by using a more complex PICwhich also allows for the configuration of the attenuation, ATT1 . . .ATT3 in FIG. 2, of the filter or allows for a varying tuning speed. ThisPIC directly implements most of the calculations of a classificationalgorithm based on positive and negative contributions (for exampleregression vectors) in the photonic integrated circuit. Each attenuator(ATT1 . . . ATT3 in FIG. 2) may be arranged to digitally modulate thepower of the optical signal detected by the photodetector in its opticalchain; i.e. to switch it on or off in accordance with the desiredspectral coefficient. Alternatively each attenuator may be arranged toapply an analogue amplitude modulation to the power of the opticalsignal detected by the photodetector in its optical chain, i.e. to applya spectral coefficient having a value anywhere between and including 0and 1 to the power of the optical signal detected by the photodetectorin its optical chain.

This algorithm uses for example two tunable band filters, twoattenuators and two integrating photo sensors. One optical chaincontaining band filter, attenuator and photo sensor provides thepositive contributions to the classification while the other containingits band filter, attenuator and photo sensor provides the negativecontributions to the classification. The band filters scan thewavelength range while simultaneously the attenuator is configured withthe value of the vector for that specific wavelength. If thecontribution is positive, the attenuator in the positive chain isconfigured with the value, the attenuator in the negative chain is setto zero and vice versa. The end result is the difference between thepositive and the negative photo sensor.

Because the two filter chains can be active independently, measurementspeed can be increased by only collecting at the relevant wavelengthsfor the positive/negative contribution, meaning that the positive andthe negative chain can operate in parallel, measurement speed can beincreased by only collecting at the relevant wavelengths for thepositive/negative contribution, meaning that the positive and thenegative chain can operate in parallel.

Alternatively, one can use a single chain and measure the positive andnegative contribution sequentially.

Instead of attenuation, one can also vary the time during which signalis integrated in a specific band, or a varying speed at which the bandpass filter move across the spectrum with a low speed where there is ahigh coefficient value of the regression vector and a high speed wherethere is a low coefficient, and skipping an interval where thecoefficient is zero. The algorithm based on the result consists ofsimple additions/subtractions only and thus is not processor intensive.

Whilst the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustrations and descriptionare to be considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments and can be used inother applications.

The invention is applicable for important application in healthcarespectral tissue sensing devices. However, this technology will also bebeneficial for any other area where spectroscopy is now used such asfood inspection, pollution control, crop management, in-vitrodiagnostics and analysis of chemical substances.

Summarizing the invention: Spectroscopy has proven to be able torecognize key characteristics of materials such as tissue, food,chemicals et cetera. In specific cases, not the whole spectrum is neededbut specific bands in the spectrum are sufficient to characterize aspecific substance in the material.

Currently, bulk optics (i.e. discrete optical components) are used whichdistribute the light per wavelength onto sensors using gratings orprisms. These discrete optical components require a significant amountof space and have a high cost, especially in the near infrared regiondue to the need for a linear image array of a suitable material such asInGaAs or similar materials. In addition, the full spectral data needsto be collected from such a sensor, thus increasing communication andprocessing overhead. This conflicts with the need that devices usingthese technologies are moving towards low-cost, hand-held devices.

With the recent developments of small scale embedded photonics such asphotonic integrated circuits, alternative options can be constructedthat were not possible without this technology. An example is theability to integrate multiple tunable narrow-band filters onto a singledie. The filters are tunable within milliseconds.

The present invention provides a handheld spectroscopic analysis deviceHHD (as an add-on to for example a tablet computer, smart phone or smartwatch) that uses the tuning of fast tunable filters on a single photonicintegrated circuit according to a stored table with wavelengths andspectral coefficients by a simple microcontroller. Calculation of thespectroscopic analysis end result is done with photodetectors such asphotodiodes and summation of the resulting signals only, therebyreplacing a substantial part of the discrete optical components of sucha device and reducing the total amount of data processed.

Due to the tunable characteristics of a filter chain, many differentsubstances can be recognized by applying different filter shapes withoutrequiring changes to the hardware, allowing different applications onthe same platform.

Various embodiments of the invention are provided:

1. A spectroscopic analysis device for analysis of a sample comprising:

an input for receiving light from the sample,

a photonic integrated circuit comprising one or more tunable bandpassfilters arranged to filter the received light, and

a controller arranged

-   -   to control the one or more tunable bandpass filters,    -   to receive filter results obtained from the one or more tunable        bandpass filters, and    -   to provide spectroscopic analysis results based on the received        filter results.        2. A spectroscopic analysis device according to embodiment 1,        wherein the photonic integrated circuit comprises one or more        photodetectors, each of the photodetectors being operatively        connected to a respective one of each of the one or more tunable        bandpass filters.        3. A spectroscopic analysis device according to embodiment 2,        wherein the photonic integrated circuit comprises one or more        attenuators, each of the attenuators being connected between a        respective one of each of the one or more tunable bandpass        filters and a respective one of the one or more photodetectors.        4. A spectroscopic analysis device according to embodiment 3,        wherein the controller is arranged to control the one or more        attenuators.        5. A spectroscopic analysis device according to embodiment 1,        comprising one or more integrators, whereby each of the one or        more integrators is arranged to collect the results from a        respective one of the one or more tunable bandpass filters.        6. A spectroscopic analysis device according to embodiment 2,        comprising one or more integrators, whereby each of the one or        more integrators is connected to a respective one of the one ore        photodetectors in order to collect the results from the        respective one of the one or more tunable bandpass filters.        7. A spectroscopic analysis device according to embodiment 1,        comprising a broadband light source for illuminating the sample.        8. A spectroscopic analysis device according to embodiment 1,        comprising a display to display the spectroscopic analysis        results.

In an alternative implementation disclosed above and elaborated here inmore detail; rather than using a variable attenuator in each opticalchain to control the attenuation, attenuation may be effected in thetime domain by providing each photodetector in the optical chain with anintegrator that is configured to integrate the photodetector'selectrical output. Attenuation may be effected by either i) controllingthe time that a tunable bandpass filter in each optical chain isarranged to filter a specific wavelength interval or ii) controlling thetime during which an integrator is arranged to perform an integration ofa specific wavelength interval. Such implementations may be used in asimplified photonic integrated circuit that has no variable attenuator.Since the signal resulting from each integrator depends on both theoptical signal intensity detected by the photodetector as well as thetime that its corresponding tunable bandpass filter is set to filter aspecific wavelength interval, the signal resulting from the integratormay be adjusted through i) and/or ii) above in order to control thecontributions of each wavelength interval, i.e. spectral coefficients,to a classification algorithm. For example, if the spectral coefficientof one wavelength interval Δλ₁ is desired to be twice that of anotherwavelength interval Δλ₂; either the integration time during which theintegrator that records the signal at wavelength Δλ₁, or the time duringwhich the tunable bandpass filter is arranged to wavelength intervalΔλ₁, may be twice that as for Δλ₂. This form of optical processing bythe PIC alleviates the need for separate processing of the results ofthe contributions of each wavelength interval in a separate controller.This implementation is also compatible with the implementation having avariable attenuator in the PIC; i.e. the control of the integrator andthe bandpass filter may be used to perform some parts of the opticalprocessing, and other parts of the optical processing may be performedby a variable attenuator.

The following examples may also be used:

1. A spectroscopic analysis device for analysis of a sample comprising:

a photonic integrated circuit (PIC) comprising:

an input (DEF) for receiving light from the sample; and

a demultiplexer (DEMUX) arranged to distribute the received light intoat least a first optical chain (C1) and a second optical chain (C2);

wherein each optical chain (C1, C2) of the photonic integrated circuit(PIC) further comprises a tunable bandpass filter (TBF1, TBF2) and aphotodetector (PD1, PD2) arranged respectively to filter and to detectthe light distributed into its corresponding optical chain (C1, C2);

wherein each optical chain (C1, C2) further comprises an integrator(INT1, INT2) configured to integrate an electrical output of thephotodetector in its corresponding optical chain (C1, C2);

wherein i) each tunable bandpass filter (TBF1, TBF2) is configured toreceive control data indicative of a time period (T_(Filter)) duringwhich the corresponding tunable bandpass filter (TBF1, TBF2) is arrangedto filter a predetermined wavelength interval and/or ii) each integrator(INT1, INT2) is configured to receive control data indicative of a timeperiod (T_(Int)) during which the corresponding integrator is arrangedto integrate an electrical output of its corresponding photodetector(PD1, PD2), such that the integration result of the correspondingintegrator (INT1, INT2) is controlled based on the respective timeperiod (T_(Filter), T_(Int)).

2. A spectroscopic analysis device according to example 1 furthercomprising

a controller (MC) arranged:

-   -   to control the two or more tunable bandpass filters (TBF1,        TBF2),    -   to control the two or more integrators (INT1, INT2),    -   to receive integrator results obtained from the two or more        integrators (INT1, INT2), and    -   to provide spectroscopic analysis results based on the received        integrator results.        3. A spectroscopic analysis device according to example 2        wherein the controller (MC) further comprises a memory (MWCWT)        configured to store a plurality of spectral coefficients        indicative of both i) wavelength intervals to be filtered and        either ii) time periods (T_(Filter)) during which a filter is        arranged to filter a predetermined wavelength interval, or iii)        time periods (T_(Int)) during which an integrator is arranged to        integrate an electrical output of its corresponding        photodetector (PD1, PD2); and wherein the controller (MC) is        further configured to control a result of the integrator (INT1,        INT2) in each optical chain (C1, C2) by applying the spectral        coefficients to the respective two or more bandpass filters        (TBF1, TBF2) or to the respective two or more integrators (INT1,        INT2).        4. A spectroscopic analysis device according to any one of        examples 2 to 3 wherein the controller (MC) is further arranged        to process the received photodetector results based on the        difference or the ratio between i) the integrator results        received from the integrator of the first optical chain (C1)        and ii) the integrator results received from the from the        integrator of the second optical chain (C2).        5. A spectroscopic analysis device according to example 2        wherein the controller (MC) is further arranged to control each        tunable bandpass filter (TBF1, TBF2) by stepping each tunable        bandpass filter (TBF1, TBF2) across a predetermined wavelength        range of interest.        6. A spectroscopic analysis device according to example 5        wherein the stepping comprises i) arranging a tunable bandpass        filter (TBF1, TBF2) to filter a plurality of wavelength        intervals (Δλ₁, Δλ₂) such that a first wavelength interval (Δλ₁)        is filtered by the tunable bandpass filter (TBF1, TBF2) during a        first time period (T_(Filter) _(_) ₁) and such that a second        wavelength interval (Δλ₂) is filtered by the tunable bandpass        filter (TBF1, TBF2) during a second time period (T_(Filter) _(_)        ₂); wherein first time period (T_(Filter) _(_) ₁) and the second        time period (T_(Filter) _(_) ₁) differ by a factor of at least        1.1; and/or ii)        arranging an integrator (INT1, INT2) to integrate an electrical        output of its corresponding photodetector (PD1, PD2) such that        electrical signals output by the photodetector (PD1, PD2)        corresponding to optical wavelengths at a plurality of        wavelength intervals (Δλ₃, Δλ₄) are integrated by integrating        electrical signals corresponding to optical wavelengths within a        third wavelength interval (Δλ₃) during a third time period        (T_(Int) _(_) ₃) and by integrating, with the same integrator        (INT1, INT2), electrical signals corresponding to optical        wavelengths within a fourth wavelength interval (Δλ₄) during a        fourth time period (T_(Int) _(_) ₄); and wherein the third time        period (T_(Int) _(_) ₃) and the fourth time period (T_(Int) _(_)        ₄) differ by a factor of at least 1.1.        7. A spectroscopic analysis device according to example 2        wherein the controller (MC) is further arranged to control the        tunable bandpass filter (TBF1, TBF2) in each optical chain (C1,        C2) by setting the tunable bandpass filter (TBF1, TBF2) in each        optical chain (C1, C2) to provide an individual optical chain        spectral transmission characteristic which when summed together        for both optical chains provide a combined spectral transmission        characteristic that is coincident with one or more optical        emission lines or reflectance bands or absorption bands in a        spectrum of the sample.        8. A spectroscopic analysis device according to example 2        wherein the controller (MC) is further arranged to control each        tunable bandpass filter (TBF1, TBF2) and each integrator (INT1,        INT2) by:

tuning each filter (TBF1, TBF2) to a start of a wavelength sub-range tobe integrated;

resetting each output of each integrator (INT1, INT2);

measuring and storing the accumulated charge of the each integrator; andreading-out the accumulated charge of each integrator using an Analogueto Digital converter (MUXADC).

9. A spectroscopic analysis device according to example 8 wherein thecontroller (MC) is further arranged to control each tunable bandpassfilter (TBF1, TBF2) by scanning each tunable bandpass filter across apredetermined range of wavelengths starting at the wavelength sub-range.10. A spectroscopic analysis device according to example 3 wherein the(MC) is further arranged to generate a tissue classification indicativeof a tissue type; wherein the tissue classification is generated by:

multiplying each integrator result by a spectral coefficient stored inthe memory of the controller (MWCWT); and

combining two or more multiplied integrator results through addition,subtraction multiplication or division.

11. A spectroscopic analysis device according to example 1, furthercomprising a broadband light source (4WTHS) for illuminating the sample.

12. A spectroscopic analysis device according to example 1, comprising adisplay (D) configured to display the spectroscopic analysis results.

13. A spectroscopic analysis device according to example 1 wherein eachtunable bandpass filter (TBF1, TBF2) is an optical ring resonator or aMach-Zehnder interferometer.

14. A spectroscopic analysis device according to example 1 or example 2wherein each optical chain (C1, C2) of the photonic integrated circuit(PIC) further comprises a variable attenuator (ATT1, ATT2) arranged toattenuate the light distributed into its corresponding optical chain(C1, C2); wherein the attenuator is disposed between the demultiplexer(DEMUX) and the respective photodetector (PD1, PD2) in each opticalchain (C1, C2).15. Computer program product comprising instructions which when executedon a controller of the spectroscopic analysis device of example 2 causethe controller (MC) to perform the method steps of:

-   -   controlling the two or more tunable bandpass filters (TBF1,        TBF2);    -   controlling the two or more integrators (INT1, INT2),    -   receiving integrator results obtained from the two or more        integrators (INT1, INT2); and    -   providing spectroscopic analysis results based on the received        integrator results;    -   wherein the controller (MC) is configured to control the results        of the one or more integrators (INT1, INT2) by applying spectral        coefficients indicative of i) wavelength intervals to be        filtered and either ii) time periods (T_(Filter)) during which a        filter is arranged to filter a predetermined wavelength        interval, or iii) time periods (T_(Int)) during which an        integrator is arranged to integrate an electrical output of a        corresponding photodetector (PD1, PD2).

The invention claimed is:
 1. A spectroscopic analysis device foranalysis of a sample of a substance based on a classification algorithmhaving a plurality of spectral coefficients that each correspond to acontribution to the classification algorithm from a wavelength interval,the device comprising: an input for receiving light from the sample, aphotonic integrated circuit comprising: one or more tunable bandpassfilters arranged to filter the received light, and one or morephotodetectors; wherein each of the photodetectors is operativelyconnected to a respective one of each of the one or more tunablebandpass filters; and wherein each photodetector further comprises anintegrator that is configured to integrate an electrical output of thecorresponding photodetector, and a controller arranged to control theone or more tunable bandpass filters, to control the one or moreintegrators; to receive, from each integrator, filter results obtainedfrom the one or more tunable bandpass filters, wherein the controller isfurther arranged to provide spectroscopic analysis results of the samplebased on the filter results received from each integrator and based onthe classification algorithm by either i) attenuating the filteredreceived light detected by the one or more photodetectors in accordancewith the plurality of spectral coefficients by controlling the timeduring which each tunable bandpass filter filters each wavelengthinterval or ii) attenuating the integrated signal received from eachintegrator in accordance with the plurality of spectral coefficients bycontrolling the time during which each integrator integrates eachwavelength interval.
 2. A spectroscopic analysis device according toclaim 1 further comprising a broadband light source for illuminating thesample.
 3. A spectroscopic analysis device according to claim 1 furthercomprising a display to display the spectroscopic analysis results.
 4. Aspectroscopic analysis device according to claim 1 further comprising amicrocontroller including a memory; wherein the memory is configured tostore the plurality of spectral coefficients.
 5. A spectroscopicanalysis device according to claim 4 having at least two tunablebandpass filters, at least two photodetectors, at least two integrators,and further comprising an analogue to digital converter; wherein theanalogue to digital converter is connected to the outputs of the atleast two integrators and is configured to convert, in a multiplexedmanner, the outputs of the at least two integrators into electricalsignals that correspond to the amount of light detected by eachcorresponding photodiode.
 6. A method of operating the spectroscopicanalysis device of claim 4 comprising the steps of: tuning a tunablebandpass filter to a start of a wavelength sub range to be integrated,resetting the corresponding integrator, measuring and storing anaccumulated charge in the integrator, stopping the measuring andreading-out the accumulated charge using the analogue to digitalconverter, executing a classification algorithm for a sample of asubstance by repeating the steps of tuning, resetting, measuring andstopping for each of the plurality of spectral coefficients to generatea plurality of intermediate results, and summing the intermediateresults.